Reflective color filter, and reflective color display apparatus and method of color display employing the same

ABSTRACT

A reflective color filter, and a reflective color display apparatus and a method for a reflective color display employing the reflective color filter is provided. The reflective color filter includes first and second photonic crystal areas which reflect light in a selection wavelength band from external light and include a tunable photonic crystal which tunes a photonic band gap corresponding to a frequency bandwidth reflecting light through stimulation. A controller provides stimulations to the first and second photonic crystal areas to adjust the photonic band gap of the tunable photonic crystal of the first and second photonic crystal areas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2010-0124228, filed on Dec. 7, 2010, in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference for all purposes.

BACKGROUND

1. Field

The following description relates to reflective color filters, andreflective color display apparatuses and methods of a color displayemploying the same.

2. Description of the Related Art

Generally, a color may be formed using three primary colors which arered, green, and blue (RGB). To form a color with RGB, three coloredlight beams (a red color light beam, a green color light beam, and ablue color light beam) may be superimposed. A conventional color displayapparatus may display color by dividing an area of a fixed threeprimary-color filter and transmitting or reflecting light on the dividedareas of the fixed three primary-color filter.

The conventional color display apparatus may use an absorption typecolor filter which transmits only a desired color and absorbs the othercolors. In the conventional color display apparatus, for example, lossof light passing through the absorption type color filter may be largewhich may affect a display image. Also, since the absorption type colorfilter may be used by dividing the area when a primary color or a colorclose to the primary color is displayed, light passing through othercolor areas may be completely blocked out. As such, more light may belost when using the absorption type color filter and thus, affecting theoverall display image.

Thus, when the absorption type color filter is used in a reflectivecolor display apparatus, a loss ratio of the absorption type colorfilter is generally too large with respect to its reflectivecharacteristics. As such, it becomes difficult to display a bright colorwhen using the absorption type color filter.

As an alternative to the absorption type color filter, a color filterusing a photonic crystal having reflective characteristics in which thecolor filter may be capable of reflecting a color corresponding to aphotonic band gap and transmitting other colors has been studied. Forexample, a primary color displayed with a photonic crystal may be ashiny and bright color that may not be displayed by the conventionalcolor filter. However, although a photonic crystal color filter may becapable of solving the problem of large light loss of a reflective colordisplay apparatus using an absorption type color filter, a three primarycolor display principle may still be used to display the color areas ona color coordinate that a user recognizes. Therefore, color loss maystill arise with respect to an area-division of a color filter employingthe three primary color display principle.

SUMMARY

In one general aspect, there is provided a reflective color filter whichinclude first and second photonic crystal areas which reflect light in aselection wavelength band from external light and include tunablephotonic crystal which tunes a photonic band gap corresponding to afrequency bandwidth reflecting light through stimulation, and acontroller which provides stimulations to the first and second photoniccrystal areas to adjust the photonic band gap of the tunable photoniccrystal of the first and second photonic crystal areas.

The reflective color filter may further include an absorption platedisposed under the first and second photonic crystal areas.

The first and second photonic crystal areas may include the tunablephotonic crystal so that at least one of a shape, a volume, and aneffective refractive index of each of the first and second photoniccrystal areas may be changed by an external stimulation to change acentral frequency of the photonic band gap.

The first and second photonic crystal areas may be arrayed side-by-sidein a horizontal direction.

The reflective color filter may further include a photonic crystal panelincluding the first and second photonic crystal areas formed in eacharea corresponding to a pixel of a display apparatus to have a2-dimensional (2D) array of the first and second photonic crystal areas.

The first and second photonic crystal areas may overlap.

The reflective color filter may further include a first photonic crystalpanel including the first photonic crystal area in each areacorresponding to a pixel of a display apparatus and a second photoniccrystal panel including the second photonic crystal area in each areacorresponding to a pixel of the display apparatus, so that the first andsecond photonic crystal panels overlap.

In another aspect, there is provided a reflective color displayapparatus which include a reflective color filter which includes firstand second photonic crystal areas and a controller, and a 2D array of anarea including the first and second photonic crystal areas correspondingto a pixel, wherein the first and second photonic crystal areas reflectlight of a selection wavelength band from external light and includetunable photonic crystal capable of tuning a photonic band gapcorresponding to a frequency bandwidth reflecting light through astimulation, and the controller provides stimulations to the first andsecond photonic crystal areas to adjust the photonic band gap of thetunable photonic crystal of the first and second photonic crystal areas,and a shutter which changes transmissivity of light to variably adjustamounts of lights incident onto the first and second photonic crystalareas.

The reflective color display apparatus may further include a photoniccrystal panel including the first and second photonic crystal areaswhich are arrayed side-by-side in a horizontal direction and formed ineach area corresponding to a pixel to have a 2D array of a pair of thefirst and second photonic crystal areas.

The reflective color display apparatus may further include a firstphotonic crystal panel including the first photonic crystal area in eacharea corresponding to a pixel and a second photonic crystal panelincluding the second photonic crystal area in each area corresponding toa pixel, so that the first and second photonic crystal panels overlap,wherein the shutter may include a first shutter located on a side ontowhich external light is incident and a second shutter located betweenthe first and second photonic crystal panels to overlap with the firstand second photonic crystal panels.

The reflective color filter may further include an absorption platedisposed under the first and second photonic crystal areas.

The first and second photonic crystal areas may include the tunablephotonic crystal so that at least one of a shape, a volume, and aneffective refractive index of each of the first and second photoniccrystal areas is changed by an external stimulation to change a centralfrequency of the photonic band gap.

In yet another aspect, there is provided a method of a color imagedisplay using a reflective color display apparatus including providingstimulations to first and second photonic crystal areas of thereflective color apparatus to tune a photonic band gap of a tunablephotonic crystal of the first and second photonic areas and driving ashutter to variably adjust the amounts of the lights incident onto thefirst and second photonic crystal areas.

The reflective color display apparatus may include a photonic crystalpanel which includes first and second photonic crystal areas arrayedside-by-side in a horizontal direction and formed in each areacorresponding to a pixel to have a 2D array of a pair of the first andsecond photonic crystal areas.

The reflective color display apparatus may include a first photoniccrystal panel comprising the first photonic crystal area in each areacorresponding to a pixel and a second photonic crystal panel includingthe second photonic crystal area in each area corresponding to a pixel,so that the first and second photonic crystal panels overlap, whereinthe shutter includes a first shutter located on a side onto whichexternal light is incident and a second shutter located between thefirst and second photonic crystal panels to overlap with the first andsecond photonic crystal panels.

The first and second photonic crystal areas include the tunable photoniccrystal so that at least one of a shape, a volume, and an effectiverefractive index of each of the first and second photonic crystal areasmay be changed by an external stimulation to change a central frequencyof the photonic band gap.

The reflective color filter further includes an absorption platedisposed under the first and second photonic crystal areas.

The controller may independently provide stimulations to the first andsecond photonic crystal areas to adjust the photonic band gap of thetunable photonic crystal of the first and second photonic crystal areasso that a desired color through a combination of selection wavelengthbands reflected from the first and second photonic crystal areas may bedisplayed.

In yet another aspect, there is provided a method of displaying a colorimage using a reflective color filter having first and second photoniccrystal areas, the method include reflecting, via the first and secondphotonic crystal areas having a tunable photonic crystal, light in aselection bandwidth from an external light, and providing stimulationsto the first and second photonic crystal areas to adjust a photonic gapof the tunable photonic crystal so that the tunable photonic crystalreflects light having a desired wavelength to display a desired color.

The method may further include driving a shutter to variably adjust anamount of light incident onto the first and second photonic crystalareas.

In yet another aspect, there is provided a reflective color filter whichmay include a photonic crystal area to reflect light in a selectionwavelength band from external light, the photonic crystal areacomprising a tunable photonic crystal to tune a photonic band gapcorresponding to a frequency bandwidth reflecting light throughstimulation, and a controller to provide stimulation to the photoniccrystal area to adjust the photonic band gap of the tunable photoniccrystal of the photonic crystal area to display a desired color througha combination of selection wavelength bands reflected from the photoniccrystal area.

In yet another aspect, there is provided a display apparatus including areflective color filter provided in a housing of the display apparatus,the reflective color filter including first and second photonic crystalareas which reflect light in a selection wavelength band from externallight and comprise a tunable photonic crystal which tunes a photonicband gap corresponding to a frequency bandwidth reflecting light througha stimulation, and a controller which provides stimulations to the firstand second photonic crystal areas to adjust the photonic band gap of thetunable photonic crystal of the first and second photonic crystal areas.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating structures of a reflective color filterand a reflective color display apparatus employing the reflective colorfilter, according to an example embodiment.

FIG. 2 is a diagram illustrating color coordinates, showing possiblecombinations of color coordinates displaying a white color.

FIG. 3 is a diagram illustrating a color coordinate model that issimplified as a semicircular model.

FIG. 4 is a diagram illustrating a method of displaying a color of acolor area that is displayed at the brightest brightness and a color ofa color area that is not displayed at the brightest brightness.

FIG. 5 is a diagram illustrating a reflective color filter having anoverlap type structure and a reflective color display apparatusemploying the reflective color filter, according to another exampleembodiment.

FIG. 6 is a diagram illustrating an existing structure that divides apixel area into three pixel areas and displays colors of the three pixelareas with a three primary color filter.

FIG. 7 is a diagram illustrating a structure that divides a pixel areadisplaying a color of an area-division type variable pixel into twopixel areas so as to correspond to FIG. 1.

FIG. 8 is a diagram illustrating a structure in which two variablepixels overlap each other to achieve a color display of an overlap typevariable pixel so as to correspond to FIG. 5.

FIG. 9 is a graph illustrating a brightness characteristic of a colordisplay apparatus according to the color display methods of FIGS. 6through 8.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand description of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. Accordingly, various changes,modifications, and equivalents of the systems, apparatuses and/ormethods described herein will be suggested to those of ordinary skill inthe art. Also, descriptions of well-known functions and constructionsmay be omitted for increased clarity and conciseness.

A reflective color filter, and a reflective color display apparatusemploying the same may use a variable color tunable photonic crystalcapable of changing a photonic band gap area in real time through anexternal stimulation. According to the reflective color filter and thereflective color display apparatus and method that will be describedbelow, a display color may be changed along a curve approximate to anedge of a color coordinate corresponding to a full primary color usingthe tunable photonic crystal. Also, arbitrary dots on a display colorcurve may be displayed in an analog form through a driving circuit.

All colors on a color coordinate system may be displayed through anappropriate mixture ratio of three primary colors on a three primarycolor display coordinate. To display all colors including white andblack colors that a user recognizes on a color coordinate system, anarbitrary dot on the color coordinate may be displayed through a mixtureof two colors at which a straight line passing a desired colorcoordinate meets a display color curve. Differently from theconventional three primary color display method by which fixed threeprimary colors are determined, when the above-described color displaymethod is used, an arbitrary color on the color coordinate may bedisplayed through two colors. As such, loss of light in a color filtermay be reduced due to a three-area division principle. Since examples ofthe method of displaying the color coordinate through two colors mayinclude various types of methods, a driving circuit may be configured toselect a color display combination of displaying a maximum brightnessthrough selections of an appropriate driving mechanism and a colordisplay algorithm.

The reflective color display apparatus according to an exampleembodiment may display clearer and brighter primary colors andcombination colors than the conventional reflective color displayapparatus using the absorption type color filter. Therefore, thereflective color display apparatus may be capable of displaying a shiny,bright color display providing a more natural world appearance and viewto a user that cannot be expressed by conventional transmissive andreflective display apparatuses. Also, the reflective color displayapparatus according to an example embodiment of the present inventionmay use external light as a light source. As such, the reflective colordisplay apparatus may contribute to the development of color displayapparatuses that consume less power and may have more simplifiedstructures.

FIG. 1 illustrates structures of a reflective color filter and areflective color display apparatus employing the reflective colorfilter, according to an example embodiment.

Referring to FIG. 1, the reflective color display apparatus includes areflective color filter 1 and a shutter 30 which may variably tune anamount of light incident onto the reflective color filter 1. Thereflective color filter 1 includes a photonic crystal panel 10 and acontroller 50. The photonic crystal panel 10 includes first and secondphotonic crystal areas 11 and 13 to reflect light in a selectionwavelength band from external light. The controller 50 provides anexternal stimulation to the first and second photonic crystal areas 11and 13 of the photonic crystal panel 10 to control a photonic band gapof a photonic crystal. Photonic crystals, for example, may be periodicdielectric structures that have a band gap that may prevent propagationof a certain frequency range of light. As such, a user may be capable ofcontrolling light more efficiently when using photonic crystals.

The reflective color filter 1 may reflect all of the light in a selectedwavelength band and transmit light of other wavelength bands. Therefore,the reflective color filter 1 may not require a reflective minor that isgenerally required when an absorption color filter is used. However, thereflective filter 1 may include an absorption plate 20 having a blackcolor. The absorption plate 20 blocks an upward reflection of acomplementary colored light passed through the reflective color filter1. The absorption plate 20 may be included in the reflective colorfilter 1 or the reflective color display apparatus.

The shutter 30 may variably change a transmissivity of the light tovariably adjust the amounts of lights respectively incident onto thefirst and second photonic crystal areas 11 and 13 of the photoniccrystal panel 10. In other words, the shutter 30 may include first andsecond shutter areas 31 and 33 that respectively adjust the amounts ofthe lights incident onto the first and second photonic crystal areas 11and 13.

For non-limiting illustration purposes, FIG. 1 illustrates thereflective color filter 1 and the shutter 30 located in an areacorresponding to one pixel of the reflective color display apparatus.The photonic crystal panel 10 may include the first and second photoniccrystal areas 11 and 13 that are arranged side-by-side in a horizontaldirection for each pixel. When the photonic crystal panel 10 is appliedto the reflective color display apparatus, the reflective color filter 1may include the photonic crystal panel 10 that includes the pair of thefirst and second photonic crystal areas 11 and 13 that are2-dimensionally arrayed to correspond to a 2-dimensional (2D) pixelarray of the reflective color display apparatus. In other words, in thereflective color filter 1, the photonic crystal panel 10 may have a 2-Darray of the pair of the first and second photonic crystal areas 11 and13 so that the first and second photonic crystal areas 11 and 13 arelocated in each area corresponding to one pixel of the reflective colordisplay apparatus. Accordingly, the shutter 30 may include each pair ofshutter areas in each pixel to adjust the amounts of the lightsrespectively incident onto the first and second photonic crystal areas11 and 13 located in each pixel. In other words, the shutter 30 may havea 2-D array of the pair of the first and second shutter areas 31 and 33corresponding to the 2-D array of the pair of the first and secondphotonic crystal areas 11 and 13.

In FIG. 1, the first and second photonic crystal areas 11 and 13 arearrayed side-by-side in the horizontal direction but may be arrayed tohave an overlap structure as described below with reference to FIG. 5.

In the photonic crystal panel 10, the first and second photonic crystalareas 11 and 13 may include a tunable photonic crystal, (that is, avariable color tunable photonic crystal). The tunable photonic crystalmay be provided so that a photonic band gap corresponding to a frequencybandwidth reflecting light through stimulation is tuned.

A shape, a size, or an effective refractive index of the tunablephotonic crystal may vary with external electric or mechanicalvariations so that the tunable photonic crystal may tune the photonicband gap corresponding to the frequency bandwidth reflecting light.

The tunable photonic crystal may vary the photonic band gap from aninfrared light to an ultraviolet light according to an externalstimulation. A color filter, which becomes transparent when a photonicband gap of such a tunable photonic crystal is used under an ultravioletor infrared area, may be embodied.

The tunable photonic crystal applied to the first and second photoniccrystal areas 11 and 13, for example, may be photonic crystalsdistributed in nanoparticle crystal of a high refractive index that isdielectric within a peripheral environment in which a volume varies dueto infiltration of an electrolyte caused by a reversible oxidoreductionreaction induced by a voltage.

The controller 50 independently provides stimulations to each of thefirst and second photonic crystal areas 11 and 13 of the photoniccrystal panel 10 to adjust the photonic band gap of the tunable photoniccrystals of the first and second photonic crystal areas 11 and 13. As aresult, a desired color may be displayed through a combination ofselection wavelengths reflected from the first and second photoniccrystal areas 11 and 13.

In FIG. 1, electrodes 41 a, 41 b, 41 c, 43 a, 43 b, and 43 c areprovided above the shutter 30, between the shutter 30 and the photoniccrystal panel 10, and under the photonic crystal panel 10. Thus, theelectrodes 41 a, 41 b, 41 c, 43 a, 43 b, and 43 c electrically connectbetween the controller 50, the shutter 30, and the photonic crystalpanel 10 to one another so that the shutter 30 and the photonic crystalpanel 10 are controlled by the controller 50. The electrodes 41 a, 41 b,41 c, 43 a, 43 b, and 43 c are provided to correspond to the arrays ofthe pair of the first and second shutter areas 31 and 33 of the shutter30 and the pair of the first and second photonic crystal areas 11 and 13of the photonic crystal panel 10. As mentioned above, the pair of thefirst and second shutter areas 31 and 33 of the shutter 30 and the pairof the first and second photonic crystal areas 11 and 13 of the photoniccrystal panel 10 constitute one pixel of the reflective color displayapparatus. In FIG. 1, the electrodes 41 b and 43 b located between theshutter 30 and the photonic crystal panel 10 may be commonly used.Alternatively, an electrode positioned under the shutter 30 and anelectrode positioned above the photonic crystal panel 10 may beseparately provided.

As described above, the reflective color display apparatus may includethe reflective color filter 1 including one photonic crystal panel 10and one shutter 30. Also, the photonic crystal panel 10 and the shutter30 may be provided so that two photonic crystal areas and two shutterareas are provided in one pixel to correspond to one another.

According to the reflective color display apparatus, stimulations areindependently provided to each the first and second photonic crystalareas 11 and 13 of the photonic crystal panel 10 of the reflectivefilter 1 so that the reflective color display apparatus may display acolor image. Therefore, the photonic band gap of the tunable photoniccrystals of the first and second photonic crystal areas 11 and 13 may betuned by reflecting a light of a desired wavelength. When the photonicband gap is being tuned, the shutter 30 may be driven to variably adjustthe amounts of the lights incident onto the first and second photoniccrystal areas 11 and 13, thereby displaying a desired color image to adesired brightness.

A principle of realizing a desired color through the photonic crystalpanel 10 including the first and second photonic crystal areas 11 and 13independently tuned in each pixel may be described as follows.

FIG. 2 illustrates color coordinates, showing possible combinations ofcolor coordinates displaying a white color. In FIG. 2, R, G, and Brespectively denote red, green, and blue colors that are three primarycolors.

Referring to FIG. 2, when arbitrary dots on the color coordinate systemare to be displayed by a combination of particular colors, two primarycolors corresponding to vertexes of a line segment (for example, A1, A2and B1, B2) may at least be provided. When a color is displayed througha combination of two colors, there may exist various methods forselecting primary colors.

Therefore, in contrast to providing only a linear combination determinedto display an arbitrary color coordinate as in the conventional threeprimary color model, an optimal one of possible two color linearcombinations may be selected. As such, the brightest of the colorcombinations may be selected. The following two points may beconsidered, for example, to obtain more favorable displaycharacteristics.

First, several primary color combinations are possible to display thesame color coordinate but these combinations may have differentbrightness characteristics from one another. Therefore, the brightestcombination may be selected among the primary color combinations.

Secondly, a color change amount of a variable device such as, forexample, a variable color tunable photonic crystal device, may beproportional to a response speed thereof. Therefore, when a displaycolor changes from one color to another color, it may be considered thatshortening of a movement length of a color coordinate is more favorablefor a moving picture display.

FIG. 3 illustrates a color coordinate model that is simplified as asemicircular model. In FIG. 3, color ranges of possible two color pixelscapable of displaying an arbitrary inner color coordinate are shown. Aleft end of the semicircular model of FIG. 3 denotes a blue color Blimit, and a right end denotes a red color R limit. In FIG. 3, a° and b°denote arbitrary values from the B limit and the R limit, respectively.Here, a two color pixel, for example, indicates that one pixel may bedivided into two color areas.

As shown in FIG. 3, a straight line passing an arbitrary dot in asemi-circle may have an arbitrary value in a range reaching from a leftend (the B limit) of the semi-circle to a right end (the R limit) of thesemi-circle.

Here, based on a desired color coordinate, a ratio between lengths of aleft line segment and a right line segment of the desired colorcoordinate monotone decreases as a left dot of a line segment moves fromthe B limit to a green color, and only one combination having a colorcoordinate at the center of the line segment exists.

In a reflective type color display apparatus, the brightest brightnessthat a color display device may display with respect to incident lightmay be fixed by reflectivity. Therefore, to adjust a ratio betweenintensities of colors in a two color pixel, a reflection intensity ofone device may be reduced so that the other device is dark. It isfavorable that relative brightness of two colors is to be most similarto each other to obtain the brightest brightness on a desired colorcoordinate. Thus, a pixel combination having the brightest brightness ona provided color coordinate is marked with a dashed line in FIG. 3.

Accordingly, when a color is displayed so that a desired colorcoordinate is shown in a center of a line segment formed by the color ofthe two color pixels to obtain the brightest brightness, only the colorof the two color pixels with respect to the desired color coordinate maybe determined. Thus, when a color display algorithm is realized usingthis method, a color display device displaying the brightest brightnessmay be obtained.

However, all color areas may be not displayed using this method.

FIG. 4 illustrates a method of color display of a color area that isdisplayed at the brightest brightness and a color area that is notdisplayed at the brightest brightness. In FIG. 4, an area of a largesemi-circle indicated with diagonal lines corresponds to a color areathat is displayed at the brightest brightness, and two smallsemi-circles correspond to a color area that is not displayed at thebrightest brightness.

An area that is not displayed with a central coordinate may be displayedas follows.

In other words, when a color coordinate to be displayed is located in aleft quarter circle area of a semi-circle, one of two color pixels isfixed to a B limit, and only a reflection intensity of the one pixel maybe adjusted. Also, the other one of the two color pixels may bedisplayed by changing only a color of another quarter semi-circle(between green and red colors) corresponding to the other pixel withouta change of reflectivity thereof.

When the color coordinate is located in a right quarter circle area(between red and green colors), one of the two color pixels is fixed tothe R limit, and only a reflection intensity thereof may be adjusted.Also, only a color of the other one of the two color pixels may bechanged between red and green color areas without changing thereflection intensity.

When a color area is displayed using the above-described method,brightness may be slightly reduced.

As described above, when all color coordinates in a color coordinatearea are displayed by linear combinations, change of a relativeintensity between two primary colors may be required. The first andsecond shutter areas 31 and 33 of the shutter 30 for adjusting anintensity of light are located above the first and second photoniccrystal areas 11 and 13 constituting two color pixels. Therefore, when areflective color filter and a reflective color display apparatus areconfigured as shown in FIG. 1, all colors in a color coordinate aredisplayed using two color pixels.

As described above, the first and second photonic crystal areas 11 and13 constituting one pixel may be arrayed side-by-side in the horizontaldirection. As such, the reflective color filter 1 and the shutter 30 maybe provided in an area-division structure. However, examples in whichthe first and second photonic crystal areas 11 and 13 constituting onepixel in an arrayed side-by-side manner in the horizontal directionshould not be limited thereto. For example, the reflective color filter1 and the reflective color display apparatus may use a photonic crystalcharacteristic of reflecting only light corresponding to a selectedphotonic band gap area and transmitting other lights upwards. Therefore,the reflective filter may be arrayed in an overlap manner in a lightincident direction.

For example, a combination color in which a component of a color locatedin a lower part is darker than a color located in an upper part, may notbe displayed in the conventional color filter. In other words, thebrightness of the color in the lower part may be further reduced due tothe overlapping structure of the conventional color filter. Thus, sincethe color filter arrays having different color combinations are arrangedside-by-side to constitute one group, a structure of the conventionalcolor filter may be complicated and the color display results from useof the conventional color filter arrayed in an overlap manner may beconsiderably offset. However, the color filter according to an exampleof the present embodiment may solve the above-mentioned problems whencolor variance occurs in the color filter. Therefore, an overlap typereflective color filter and a reflective color display apparatusemploying the same may be realized with the combinations as shown inFIG. 5.

FIG. 5 illustrates a reflective color filter 1′ having an overlap typestructure and a reflective color display apparatus employing thereflective color filter 1′. In FIG. 5, elements having the same orsimilar functions as those elements of FIG. 1 are denoted by the samereference numerals, and their repeated descriptions are omitted.

Referring to FIG. 5, the reflective color display apparatus includes thereflective color filter 1′ and a shutter. The reflective color filter 1′includes first and second photonic crystal panels 10 a and 10 b thatoverlap with each other and a controller 50. The shutter includes afirst shutter 30 a that is located between the first and second photoniccrystal panels 10 and 10 b and a second shutter 30 b that is located ona side on which external light is incident. Therefore, the shutter mayvariably adjust the amounts of lights incident onto the first and secondphotonic crystal panels 10 a and 10 b.

In the overlap structure shown in FIG. 5, the first and second photoniccrystal panels 10 a and 10 b of the reflective color filter 1′respectively include an array of first photonic crystal areas 11 and anarray of second photonic crystal areas 13. The first and second photoniccrystal panels 10 a and 10 b form an overlap structure. The controller50 an external stimulation to the first and second photonic crystalareas 11 and 13 of the first and second photonic crystal panels 10 a and10 b to adjust a photonic band gap of photonic crystals.

The first shutter 30 a includes a first shutter area 31 that variablychanges transmissivity of light to variably adjust an amount of lightincident onto the first photonic crystal area 11 of the first photoniccrystal panel 10 a. The second shutter 30 b includes a second shutterarea 33 that variably changes transmissivity of light to variably adjustan amount of light incident onto the second photonic crystal area 13 ofthe second photonic crystal panel 10 b.

As shown in FIG. 5, the first photonic crystal panel 10 a, the firstshutter 30 a, the second photonic crystal panel 10 b, and the secondshutter 30 b may sequentially overlap with one another. An absorptionplate 20 having a black color may be located under the first photoniccrystal panel 10 a to block an upward reflection of a complementarycolored light having passed through the first photonic crystal area 11.As described above, the absorption plate 20 may be included as acomponent of the reflective color filter 1′ or the reflective colordisplay apparatus.

In the above-described overlap structure, the first and second photoniccrystal areas 11 and 13 and the first and second shutter areas 31 and 33may have sizes corresponding to one pixel. Also, the first photoniccrystal area 11, the first shutter area 31, the second photonic crystalarea 13, and the second shutter area 33 may overlap with one another inone pixel.

For non-limiting illustration purposes, only structures of the first andsecond photonic crystal panels 10 a and 10 b and the first and secondshutters 30 a and 30 b in an area corresponding to one pixel of thereflective color display apparatus are shown in FIG. 5. When the firstand second photonic crystal panels 10 a and 10 b and the first andsecond shutters 30 a and 30 b are applied to the reflective colordisplay apparatus, the first and second photonic crystal panels 10 a and10 b may overlap with each other so that the first and second photoniccrystal areas 11 and 13 are 2-dimensionally arrayed in the reflectivecolor filter 1′ to correspond to a 2-D pixel array of the reflectivecolor display apparatus. In other words, in the reflective color filter1′, the first photonic crystal panel 10 a may have a 2D array of thefirst photonic crystal area 11 so that the first photonic crystal area11 is located in each area corresponding to one pixel of the reflectivecolor display apparatus. The second photonic crystal panel 10 b may havea 2D array of the second photonic crystal area 13 so that the secondphotonic crystal area 13 is located in each area corresponding to onepixel of the reflective color display apparatus. Also, for example, onefirst shutter 30 a may be provided in each pixel to adjust the amount ofthe light incident onto the first photonic crystal area 11 located tocorrespond to each pixel. One second shutter 30 b may be provided ineach pixel to adjust the amount of the light incident onto the secondphotonic crystal area 13 located to correspond to each pixel. In otherwords, the first shutter 30 a may have a 2-D array of the first shutterarea 31 to correspond to the 2D array of the first photonic crystal area11, and the second shutter 30 b may have a 2D array of the secondshutter area 33 to correspond to the 2D array of the second photoniccrystal area 13.

According to the reflective color filter 1′ and the overlap structure ofthe first and second shutters 30 a and 30 b, the reflective color filter1′ may have a structure in which a pair of photonic crystal panels,including one photonic crystal area in each pixel, overlap with eachother. Similarly, the reflective color display apparatus may have astructure in which a pair of photonic crystal panels, including onephotonic crystal area in each pixel, overlap with each other. Thereflective color display apparatus may also include in the structure ashutter, including one shutter area in each pixel, on each photoniccrystal panel.

The controller 50 may independently provide stimulations to the firstand second photonic crystal areas 11 and 13 of the first and secondphotonic crystal panels 10 a and 10 b to adjust a photonic band gap oftunable photonic crystals of the first and second photonic crystal areas11 and 13. Therefore, a desired color may be displayed through acombination of selection wavelengths reflected from the first and secondphotonic crystal areas 11 and 13.

Electrodes 41 a′, 41 b′, 43 a′, 43 b′, and 43 c′ may be respectivelyprovided above the second shutter 30 b, between the second shutter 30 band the second photonic crystal panel 10 b, between the second photoniccrystal panel 10 b and the first shutter 30 a, between the first shutter30 a and the first photonic crystal panel 10 a, and under the firstphotonic crystal panel 10 a. Therefore, the electrodes 41 a′, 41 b′, 43a′, 43 b′, and 43 c′ may electrically connect the controller 50, thefirst and second shutters 30 a and 30 b, and the first and secondphotonic crystal panels 10 a and 10 b to one another so that the firstand second shutters 30 a and 30 b and the first and second photoniccrystal panels 10 a and 10 b are controlled by the controller 50. Theelectrodes 41 a′, 41 b′, 43 a′, 43 b′, and 43 c′ may be provided tocorrespond to an array of the first shutter area 31 of the first shutter30 a, the second shutter area 33 of the second shutter 30 b, the firstphotonic crystal area 11 of the first photonic crystal panel 10 a, andthe second photonic crystal area 13 of the second photonic crystal panel10 b constituting one pixel. In FIG. 5, the electrodes 43 b′, 43 a′, 41b′ respectively located between the first photonic crystal panel 10 aand the first shutter 30 a, between the first shutter 30 a and thesecond photonic crystal panel 10 b, and between the second photoniccrystal panel 10 b and the second shutter 30 b are commonly used.However, in example embodiment, for example, electrodes above and underthe first shutter 30 a, an electrode under the second shutter 30 b, anelectrode above the first photonic crystal panel 10 a, and electrodesabove and under the second photonic crystal panel 10 b may be separatelyprovided.

According to the above-described reflective color display apparatus,stimulations may be independently provided to the first and secondphotonic crystal areas 11 and 13 of the first and second photonic panels10 a and 10 b of the reflective color filter 1′ to display an image.Therefore, the photonic band gap of the tunable photonic crystals of thefirst and second photonic crystal areas 11 and 13 may be tuned in astate capable of reflecting only light having a desired wavelength. Inthis tuned state, the first and second shutters 30 a and 30 b may bedriven to variably adjust the amounts of the lights incident onto thefirst and second photonic crystal areas 11 and 13, thereby displaying adesired color image at a desired brightness.

As described above, according to the reflective color filter 1′ and thereflective color display apparatus, brightness of a color may beimproved over the conventional color display method employing the threeprimary color pixel display principle.

FIG. 6 illustrates an existing structure that divides a pixel area intothree areas and displays colors areas with a three primary color filter.FIG. 7 illustrates a structure that divides a pixel area to achieve acolor display of an area-division type variable pixel into two areas soas to correspond to FIG. 1. FIG. 8 illustrates a structure in which twovariable pixels overlap each other to achieve a color display of anoverlap type variable pixel so as to correspond to FIG. 5.

As shown in FIG. 6, when one pixel area is divided into three areas andR, G, and B color elements are disposed, each R, G, and B color mayoccupy ⅓ of the whole spectrum band, brightness of a primary color maybe limited to 1/9 of an incident white color, and brightness of thewhite may also be limited to ⅓ of the incident white color. Thisbrightness, for example, may correspond to a result where each R, G, andB color occupies ⅓ of the whole spectrum band and thus, may besubstantially reduced. As shown in FIG. 6, for example, when each R, G,and B color occupies about ⅓ of the whole spectrum band, the one pixelarea may denote a white W color.

As shown in FIG. 7, when one pixel area is divided into two areas, andspectrum bandwidths for displaying the same primary color are equal toeach other, brightness of the primary color may be ⅓ of an incidentwhite color, and brightness of the white may also be ⅓ of the incidentwhite color as a result of the spectrum width of the one pixel areabeing divided into two areas. Therefore, the brightness of the primarycolor in the color filter according to the present embodiment mayincrease three times in comparison with the brightness of theconventional three primary color filter and thus, a shiny and brightcolor may be displayed. The brightness of the white color may depend ona spectrum width when the one pixel area is area-divided does into twoareas. As such, the brightness of the white color may not vary. However,a spectrum width of a color display apparatus may be variably adjustedto improve brightness of a white color. As shown in FIG. 7, for example,when each of any two of Yellow Y, Magenta M and Cyan C, occupy ½ of thewhole spectrum band, the one pixel area may denote a white W color.

As shown in FIG. 8, when a color filter including color variable pixelsis used in an overlap manner, a color variable range of each of theupper and lower parts of the color filter may reach from a B color to anR color. Therefore, in comparison to the brightness results as describedin FIG. 7, brightness of a primary color may be equivalent to the caseof an area-division with the one pixel being divided into two areas, butbrightness of a combination color and brightness of a white color may beimproved by two times in comparison with the case of the area-division.In other words, for example, the brightness of the primary color is ⅓ ofan incident white color, and the brightness of the white is ⅔ of theincident white color. As shown in FIG. 8, for example, when each of anytwo of Yellow Y, Magenta M and Cyan C occupy ½ of the whole spectrumband, the one pixel area may denote a white W color.

FIG. 9 is a graph illustrating a brightness characteristic of a colordisplay apparatus according to the color display methods of FIGS. 6through 8.

As shown in FIG. 9, in comparison with the conventional three colordivision method, when a color filter is configured to enable a colorvariation, brightness of a primary color may be improved by at least twotimes, and brightness of a combination color may also be improved.Further, when the color filter is used in an overlap manner, brightnessof a white color may be improved.

According to one or more aspects, reflective color filters using atunable photonic crystal to reduce color loss caused by anarea-division, and reflective color display apparatuses and methods fora color display employing the same are provided.

According to an example reflective color filter, reflective colordisplay apparatus and method of a color display employing the examplereflective color filter, brightness of a primary color may be improvedby, for example, two times, and a brightness of a combination color maybe improved in comparison with the conventional three color divisionmethod. Also, a color variable filter may be used in an overlap mannerto improve brightness of a white color.

Program instructions to perform a method described herein, or one ormore operations thereof, may be recorded, stored, or fixed in one ormore computer-readable storage media. The program instructions may beimplemented by a computer. For example, the computer may cause aprocessor to execute the program instructions. The media may include,alone or in combination with the program instructions, data files, datastructures, and the like. Examples of computer-readable media includemagnetic media, such as hard disks, floppy disks, and magnetic tape;optical media such as CD ROM disks and DVDs; magneto-optical media, suchas optical disks; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory (ROM),random access memory (RAM), flash memory, and the like. Examples ofprogram instructions include machine code, such as produced by acompiler, and files containing higher level code that may be executed bythe computer using an interpreter. The program instructions, that is,software, may be distributed over network coupled computer systems sothat the software is stored and executed in a distributed fashion. Forexample, the software and data may be stored by one or more computerreadable recording mediums. Also, functional programs, codes, and codesegments for accomplishing the example embodiments disclosed herein canbe easily construed by programmers skilled in the art to which theembodiments pertain based on and using the flow diagrams and blockdiagrams of the figures and their corresponding descriptions as providedherein.

As a non-exhaustive illustration only, a reflective color filterdescribed herein may be used in display apparatuses such as a camcorder,cellular phone, a personal digital assistant (PDA), a digital camera, aportable game console, and an MP3 player, a portable/personal multimediaplayer (PMP), a handheld e-book, a portable lab-top PC, a globalpositioning system (GPS) navigation, and devices such as a desktop PC, ahigh definition television (HDTV), an optical disc player, a setup box,and the like.

A number of examples have been described above. Nevertheless, it will beunderstood that various modifications may be made. For example, suitableresults may be achieved if the described techniques are performed in adifferent order and or if components in a described system,architecture, device, or circuit are combined in a different mannerand/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

1. A reflective color filter, comprising: first and second photoniccrystal areas which reflect light in a selection wavelength band fromexternal light and comprise a tunable photonic crystal which tunes aphotonic band gap corresponding to a frequency bandwidth reflectinglight through a stimulation; and a controller which providesstimulations to the first and second photonic crystal areas to adjustthe photonic band gap of the tunable photonic crystal of the first andsecond photonic crystal areas.
 2. The reflective color filter of claim1, further comprising: an absorption plate disposed under the first andsecond photonic crystal areas.
 3. The reflective color filter of claim1, wherein the first and second photonic crystal areas comprise thetunable photonic crystal so that at least one of a shape, a volume, andan effective refractive index of each of the first and second photoniccrystal areas is changed by an external stimulation to change a centralfrequency of the photonic band gap.
 4. The reflective color filter ofclaim 1, wherein the first and second photonic crystal areas are arrayedside-by-side in a horizontal direction.
 5. The reflective color filterof claim 4, further comprising: a photonic crystal panel comprising thefirst and second photonic crystal areas formed in each areacorresponding to a pixel of a display apparatus to have a 2-dimensional(2D) array of the first and second photonic crystal areas.
 6. Thereflective color filter of claim 1, wherein the first and secondphotonic crystal areas overlap.
 7. The reflective color filter of claim6, further comprising: a first photonic crystal panel comprising thefirst photonic crystal area in each area corresponding to a pixel of adisplay apparatus and a second photonic crystal panel comprising thesecond photonic crystal area in each area corresponding to a pixel ofthe display apparatus, so that the first and second photonic crystalpanels overlap.
 8. A reflective color display apparatus, comprising: areflective color filter which comprises first and second photoniccrystal areas and a controller, and a 2D array of an area comprising thefirst and second photonic crystal areas corresponding to a pixel,wherein the first and second photonic crystal areas reflect light of aselection wavelength band from external light and comprise a tunablephotonic crystal capable of tuning a photonic band gap corresponding toa frequency bandwidth reflecting light through a stimulation, and thecontroller provides stimulations to the first and second photoniccrystal areas to adjust the photonic band gap of the tunable photoniccrystal of the first and second photonic crystal areas; and a shutterwhich changes transmissivity of light to variably adjust amounts oflights incident onto the first and second photonic crystal areas.
 9. Thereflective color display apparatus of claim 8, further comprising: aphotonic crystal panel comprising the first and second photonic crystalareas which are arrayed side-by-side in a horizontal direction andformed in each area corresponding to a pixel to have a 2D array of apair of the first and second photonic crystal areas.
 10. The reflectivecolor display apparatus of claim 8, further comprising: a first photoniccrystal panel comprising the first photonic crystal area in each areacorresponding to a pixel; and a second photonic crystal panel comprisingthe second photonic crystal area in each area corresponding to a pixel,so that the first and second photonic crystal panels overlap, whereinthe shutter comprises a first shutter located on a side onto whichexternal light is incident and a second shutter located between thefirst and second photonic crystal panels to overlap with the first andsecond photonic crystal panels.
 11. The reflective color displayapparatus of claim 8, wherein the reflective color filter furthercomprises an absorption plate disposed under the first and secondphotonic crystal areas.
 12. The reflective color display apparatus ofclaim 8, wherein the first and second photonic crystal areas comprisethe tunable photonic crystal so that at least one of a shape, a volume,and an effective refractive index of each of the first and secondphotonic crystal areas is changed by an external stimulation to change acentral frequency of the photonic band gap.
 13. A method of a colorimage display using a reflective color display apparatus, comprising:providing stimulations to first and second photonic crystal areas of thereflective color apparatus to tune a photonic band gap of a tunablephotonic crystal of the first and second photonic areas; and driving ashutter to variably adjust the amounts of the lights incident onto thefirst and second photonic crystal areas.
 14. The method of claim 13,wherein the reflective color display apparatus comprises a photoniccrystal panel which comprises first and second photonic crystal areasarrayed side-by-side in a horizontal direction and formed in each areacorresponding to a pixel to have a 2D array of a pair of the first andsecond photonic crystal areas.
 15. The method of claim 13, wherein thereflective color display apparatus comprises a first photonic crystalpanel comprising the first photonic crystal area in each areacorresponding to a pixel and a second photonic crystal panel comprisingthe second photonic crystal area in each area corresponding to a pixel,so that the first and second photonic crystal panels overlap, whereinthe shutter comprises a first shutter located on a side onto whichexternal light is incident and a second shutter located between thefirst and second photonic crystal panels to overlap with the first andsecond photonic crystal panels.
 16. The method of claim 13, wherein thefirst and second photonic crystal areas comprise the tunable photoniccrystal so that at least one of a shape, a volume, and an effectiverefractive index of each of the first and second photonic crystal areasis changed by an external stimulation to change a central frequency ofthe photonic band gap.
 17. The method of claim 13, wherein thereflective color filter further comprises an absorption plate disposedunder the first and second photonic crystal areas.
 18. The reflectivefilter of claim 1, wherein the controller independently providesstimulations to the first and second photonic crystal areas to adjustthe photonic band gap of the tunable photonic crystal of the first andsecond photonic crystal areas so that a desired color through acombination of selection wavelength bands reflected from the first andsecond photonic crystal areas is displayed.
 19. The reflective colordisplay apparatus of claim 8, wherein the controller independentlyprovides stimulations to the first and second photonic crystal areas toadjust the photonic band gap of the tunable photonic crystal of thefirst and second photonic crystal areas so that a desired color througha combination of selection wavelength bands reflected from the first andsecond photonic crystal areas is displayed.
 20. A method of color imagedisplay using a reflective color filter having first and second photoniccrystal areas, comprising: reflecting, via the first and second photoniccrystal areas having a tunable photonic crystal, light in a selectionbandwidth from an external light; and providing stimulations to thefirst and second photonic crystal areas to adjust a photonic gap of thetunable photonic crystal so that the tunable photonic crystal reflectslight having a desired wavelength to display a desired color.
 21. Themethod of claim 20, further comprising: driving a shutter to variablyadjust an amount of light incident onto the first and second photoniccrystal areas.
 22. A reflective color filter, comprising: a photoniccrystal area to reflect light in a selection wavelength band fromexternal light, the photonic crystal area comprising a tunable photoniccrystal to tune a photonic band gap corresponding to a frequencybandwidth reflecting light through stimulation; and a controller toprovide stimulation to the photonic crystal area to adjust the photonicband gap of the tunable photonic crystal of the photonic crystal area todisplay a desired color through a combination of selection wavelengthbands reflected from the photonic crystal area.
 23. A display apparatus,comprising: a reflective color filter provided in a housing of thedisplay apparatus, the reflective color filter comprising; first andsecond photonic crystal areas which reflect light in a selectionwavelength band from external light and comprise a tunable photoniccrystal which tunes a photonic band gap corresponding to a frequencybandwidth reflecting light through a stimulation; and a controller whichprovides stimulations to the first and second photonic crystal areas toadjust the photonic band gap of the tunable photonic crystal of thefirst and second photonic crystal areas.